[b]WASHINGTON (CNN) -- Chief Justice William Rehnquist, who quietly advanced the conservative ideology of the Supreme Court under his leadership, died Saturday evening. He was 80.[/b]

The justice, diagnosed with thyroid cancer, had a tracheotomy and received chemotherapy and radiation as part of his treatment.

Supreme Court spokeswoman Kathy Arberg said Rehnquist had "continued to perform his duties on the Court until a precipitous decline in his health the last couple of days."

Then with his three children beside him, the justice died at his suburban Virginia home, a court spokeswoman said.

Rehnquist had become increasingly frail after his cancer diagnosis last October, but his office had refused to characterize the seriousness of his illness.

Meanwhile, he'd worked from home for several months and missed oral arguments in a number of cases.

President Bush learned of the death shortly before 11 p.m. ET Saturday, the White House said.

"The president and Mrs. Bush are deeply saddened by the passing of the chief justice," according to a written statement. It said Bush planned to make a statement Sunday morning.

[b]End of term, end of speculation[/b]

Rehnquist adjourned the court in late June and ended speculation about his resignation.

Hours after leaving the hospital in July following treatment for fever, he made a decree:

"I want to put to rest the speculation and unfounded rumors of my imminent retirement," he said in a written statement. "I am not about to announce my retirement. I will continue to perform my duties as chief justice as long as my health permits."

He went to work the next day.

Four months earlier, when Rehnquist joined the other justices for the first time after a break, he showed no emotion, paid sharp attention to arguments and asked eight or nine technical questions.

Despite the tracheotomy tube in his throat to help him breathe, his voice was fairly strong.

[b]A junior justice[/b]

President Nixon appointed Rehnquist to the Supreme Court in 1972, and in 1986, President Reagan tapped him as chief justice to replace Warren Burger.

In that role, he led the closed-door conferences where justices discuss and vote on cases; assigned who wrote the majority rulings; managed the docket; controlled open court arguments; and supervised the 300 or so court employees, including clerks, secretaries, police and support staff.

Rehnquist, who belonged to a loose, 5-4 conservative majority, was the second-oldest man to preside over the nation's highest court.

Early in his tenure, he often was the lone dissenter, despite the presence of two other Republican appointees.

David Yalof, a constitutional law professor at the University of Connecticut, credited Rehnquist with moving the court in a consistent, conservative direction.

"He was able, over time, to gather colleagues together cordially, manage tension, build a majority and turn them over to his point of view," Yalof said.

Rehnquist followed the legal philosophy of judicial restraint, which interprets the U.S. Constitution narrowly.

He believed the only rights the Constitution protects are those the document names specifically, and justices should consider the framers' original intent when making rulings.

Shortly after Nixon named him as an associate justice, Rehnquist and Justice Byron White were the only dissenters in the landmark Roe v. Wade case (1973), which established that a woman's right to an abortion was protected under a woman's right to privacy.

"To reach its result, the court necessarily has had to find within the scope of the 14th Amendment a right that was apparently completely unknown to the drafters of the amendment," Rehnquist wrote in his dissent.

[b]Making a mark[/b]

In 1999, Rehnquist became the second chief justice in U.S. history to preside over a presidential impeachment -- that of President Bill Clinton, who was acquitted.

Having already sat on the court for 14 years, Rehnquist quickly matured in the role of chief justice. He cut the number of cases the court agreed to hear, streamlined conferences and sought clearer, strongly reasoned opinions.

Jay Jorgensen, a former clerk for the chief justice, said it was the little things Rehnquist did that built personal trust, loyalty and respect among justices who were often sharply divided ideologically.

"He set up a system during conferences where every justice, one by one, in order of seniority, is allowed to weigh in on a case," Jorgensen said. "There is no free-for-all debate, the chief justice does not allow bickering."

Saturday night, Ruth Wedgwood, a constitutional lawyer and close friend of Rehnquist, said, "He was an interesting man. He had an interesting life. Over time, I think he became a much more unifying figure in the court."

His death, she said, puts a "great burden" on the Senate, which will be responsible for confirming a replacement.